In recent years, water resources, especially groundwater resources have experienced serious pollution, resulting in various direct or latent harm and threats to ecological systems and humans. Among these harm and threats, the heavy use of nitrogen fertilizer in agriculture and the discharge of nitrogen-containing have led to increased concentration of nitrate ion that well exceeded the threshold of waterbody self-purification. Excessive intake of nitrate ions by humans may cause serious health problems, such as birth defects, diarrhea, abdominal pain, diabetes, high blood pressure. Removing nitrate ions from water is of significant benefits. Commonly used methods for removing nitrate ions from water includes mainly biochemical method, chemical reduction method, electro-osmosis method, and adsorption method. The biochemical method has a relatively long processing cycle, and its outcome is heavily seasonally dependent. The chemical reduction method requires finicky conditions, making it difficult for large-scale application. The electro-osmosis method comes with a high processing cost that render it unfit for long-term use. The ion exchange and absorption method is considered the ideal solution because of the advantages of being simple, fast and efficient, low cost, and renewable. Guoming Cao and others have achieved relatively good result using a strong base anion exchange resin in treatment of nitrate contamination of groundwater, (Guoming cao, Mei Sheng, YuLei Fei, Kerwei, Weiwei Shi, and Yifeng Yu, ion exchange method by continuous flow process in treatment of nitrate contaminated groundwater, Water Purification Technology, 2011, 30 (5): 90-94). On the other hand, organic matter in urban sewage, wastewater, biochemical tail water, or natural waterbodies, are mainly of plant type, which produce undesirable odor and smell, degrade water quality, and generate disinfection byproducts harmful to human health during water disinfection treatment process. The prevailing effective adsorbent material for removing this type of natural organic matter is weak base anion exchange resin.
Typically, the functional group in an anion exchange resin is amino group or quaternary ammonium group, the adsorption capacity for nitrate ions is controlled by the number of functional groups in resin surface. Traditionally, in chloromethylated polystyrene-divinylbenzene polymer, when undergoing quaternization, each chloromethyl within the polymer can produce only one quaternary ammonium group. The chloromethyl content within chloromethylated polystyrene-divinylbenzene polymer is fixed (16-20% by mass) and resistant to enhancement. This results in the number of quaternary ammonium salt group in the resin surface being impervious to enhancement since it is limited by the number of chloromethyl. Therefore, it remains a difficult challenge to increase the number of the quaternary ammonium salt groups deriving from the chloromethyl on the chloromethylated polystyrene-divinylbenzene polymer.